Caption: Human hair shafts from the head, coloured scanning electron micrograph (SEM). The outer layer of hair (the cuticle) has overlapping scales of keratin. These scales are thought to prevent hairs from matting together. Hair is made up of a fibrous protein called keratin. Internally the hair shaft is divided into three concentric sheaths (layers) called the medulla, cortex and outer cuticle. Hair is non-living tissue. Hair grows from a hair root (bulb) embedded in the skin. Hair growth occurs when epidermal cells divide at the base of the root bulb. Hair is non-living tissue. Magnification: x20 when shortest axis printed at 25 millimetres.